The surfaces of medical implants and other substrates are sometimes modified to impart desired properties to the medical implant or to enhance its existing properties. For example, with orthopedic implants, where bone attaches directly to the implant, it is often desirable to enhance the implant's ability to adhere and to integrate with bone. Increased adhesion and integration tends to reduce healing time and to improve long term fixation. In other examples, the surfaces of substrates are modified to improve the wear resistance of the substrate. Increased wear resistance is desirable when the substrate articulates against opposing components, such as the head of a femoral stem articulating against the surface of a femoral component of a knee replacement.
Medical implant substrates are often made of metals including titanium or cobalt because these metals have advantageous chemical, physical, and mechanical properties. For example, titanium and cobalt are considered biologically inert and resist corrosion. However, implants formed from these metals typically do not have surfaces that promote satisfactory bone adhesion and fixation.
To enhance the bone adhesion and fixation, porous coatings have been applied to these alloys. Porous coatings enhance adhesion and fixation with bone by providing pores into which bone will naturally grow. The bone growth extending through the pores of the implant results in a strong, intermeshed union of bone and implant.
Examples of porous coating methods are disclosed in the following U.S. patent and patent application references, which are hereby incorporated by reference for all purposes: U.S. Pat. Nos. 4,644,942, 4,854,496, 5,034,186, 5,104,410, 5,159,007, 5,211,775, 5,308,576, 5,443,510, 5,848,350, 6,261,322, 6,534,197, 6,725,901; 6,945,448, 20040133283, 20050048193, 20050196312, 20060004466, 20060052880, 20060285991, 20070065329; and 20070068340, 20070154620, 2007196230.